This invention relates to the solvent extraction of oleaginous seed materials, and more particularly to a novel process for treating oleaginous seed materials utilizing aqueous alcohol to produce a novel protein concentrate.
Protein concentrates are presently made from oil seeds by extracting oil and at least some of the carbohydrates, leaving a residue high in protein. "Soy Protein Concentrate" is a product made in this way from dehulled soybeans so that the residual product contains at least 70% protein (dry basis). At present, Soy Protein Concentrate is made by extracting carbohydrates from so called "white flakes," which are prepared by extracting oil with hexane from dehulled, flaked soybeans and carefully desolventizing the extracted flakes so as to minimize protein denaturation. Selective extraction of carbohydrates from white flakes is now commercially accomplished by using as the solvent aqueous alcohol or slightly acidified water.
In current soybean practice, a large proportion of the soybeans are crushed to produce animal feed. The processes used comprise: cracking, at least partially dehulling, heating (conditioning), flaking, extracting with hexane, recovering solvent from the extracted flakes with heat (desolventizing), and heat treating (toasting) the desolventized flakes so as to improve the digestibility for animals. Toasting also diminishes protein solubility. Toasted meal is not deemed to be the best product for human consumption, primarily because its reduced protein solubility makes it less compatible for mixing with other food ingredients and additionally because it still contains the carbohydrates which cause flatulence.
When soybeans are to be used for human consumption, they are more carefully stored, cleaned and dehulled than are beans used for the production of animal food; and they are carefully desolventized after hexane extraction with minimal heating so as to preserve protein solubility. White flakes so made can be used directly as soy flour or extruded to make texturized vegetable protein (TVP), products which still have the disadvantage that they have a beany taste and contain the carbohydrates which cause flatulence. Partial extraction of carbohydrates from white flakes, particularly with an aqueous alcohol, produces a soy protein concentrate free of the beany taste and of those carbohydrates which cause flatulence. In U.S. Pat. No. 3,734,901 to Hayes et al, there is disclosed a process for removing such materials using an extraction medium comprised of a hydrocarbon solvent and a monohydric alcohol. The carbohydrates extracted in the production of soy protein concentrate, for which there is no present commercial use, are best disposed of by adding them to soybean meal to be used as animal feed.
Typical soybeans contain about 18.5% oil, 8.8% fiber and ash, 35.2% protein, 25.5% carbohydrates and phosphatides and 12% water. Soy Protein Concentrate is made from the beans as a residual product containing at least 70% protein (dry basis) by removing hulls, most of the oil, more than half the carbohydrates and phosphatides, and a little protein. A material balance, based on 100 parts of dry soybeans is:
______________________________________ Soybeans SPC Removed ______________________________________ Oil 21.0 0.6 20.4 Ash and fibers 10.0 3.1 6.9 Protein 40.0 38.7 1.3 Carbohydrates and Phosphatides 29.0 13.0 16.0 100.0 55.4 44.6 ______________________________________
Carbohydrates can be selectively extracted from white flakes with aqueous alcohols such as methanol, ethanol, and isopropanol, which range in concentration from 50-75% by weight. I have disclosed such a process in copending application Ser. No. 549,434, assigned to the same assignee as the present invention.
Strong alcohols have been proposed for the extraction of soybean oil from soybean flakes particularly because the product oil is semi-refined and the extracted flakes, are whiter than those extracted with hexane. However, proposed commercial processes based on alcohol extraction have had serious deficiencies; and alcohols have never been competitive with hexane as solvents for soybean oil. Although soybean oil is completely miscible with pure ethanol at its boiling point, addition of small amounts of water considerably reduces oil solubility. At the boiling temperature, and at the azeotropic composition, i.e. 95.6 weight percent ethanol, oil solubility is 13%; at 92 weight percent ethanol, oil solubility is reduced to 7%. It is not practical to extract with alcohol concentrations greater than the azeotropic, or to increase solubility by operating under pressure. Processes have been proposed which take advantage of the considerably diminished solubility of oil in cold alcohols. After cooling the miscella (solution of oil in alcohol) to precipitate oil, the separate alcohol phase can be recycled as almost the equivalent of fresh solvent, provided that the miscella is cooled to a sufficiently low temperature. These processes have failed because the miscella must be cooled to below room temperature (thus requiring refrigeration), because there is also the precipitation of a troublesome solid phase, and because it is necessary to dry the flakes to less than 3% water to avoid dilution of the recycling alcohol.
Since two separate extraction and desolventizing processes are now required for the production of soy protein concentrate, there is a need for a process capable of making a soy protein concentrate directly from full-fat flakes without an intermediate desolventizing step, using only aqueous alcohols as solvents for oil, carbohydrates and phosphatides